1. Field of the Invention
The present invention relates to an electric heating device according to the generic clause of claim 1.
2. Description of the Related Art
In motor vehicles, and in particular in motor vehicles with consumption-optimized internal combustion engines, heating devices for heating the vehicle interior and the engine are used to an increasing extent. Such heating devices are, however, also suitable for other cases of use, e.g. for room air conditioning, industrial plants and the like.
FIG. 5 shows an example where an electric heating device is used in a motor vehicle for heating the vehicle interior. Fresh air 10 taken in is heated by a blower 11 via a heating device 12 and supplied to the interior 13 of a motor vehicle. The heated air 15 flows into the vehicle interior 13 via air outlets 14a, 14b. The air to be supplied to the vehicle interior 13 can additionally be conducted over an evaporator 16a of an air-conditioning system. An electric heating device consisting of PTC heating elements preferably represents an auxiliary heating, a car heating 16b, which has its heating power supplied thereto by the vehicle engine, being normally used.
Known electric heating devices consist of a layered structure of PTC heating elements and radiator elements held in a plastic frame. The radiator elements and the PTC heating elements have provided between them electrode sheets through which the PTC heating elements are supplied with power.
These heating devices are disadvantageous insofar as, in unfavourable installation situations, metal parts, such as paper clips, coins, etc., falling through an outlet 14a into the heating/air conditioning system can come to rest on the heating element. Since the respective radiator elements are connected to ground potential and to a plus potential without being protected, the danger exists that metal parts falling into the system may cause short circuits.
DE-A1-44 36 791 discloses a heater for a heating system of a motor vehicle. The heater has a layered structure comprising corrugated ribs or corrugated fins and PTC heating tubes which are located therebetween and in which PTC heating elements are provided. The PTC heating tubes arranged in the heater consist of a thin-walled aluminium cover tube which is closed at one end thereof. This cover tube has inserted therein an insertion frame consisting of plastic material and provided with a plurality of PTC heating elements. The PTC heating elements arranged in the cover tube contact, on one side thereof, the inner wall of said cover tube and, on the other side thereof, a positive conductor arranged in said cover tube. Since the cover tube is connected to ground via the heater, the positive conductor is extended to the outside of the heating block via a special connection. An insulation is provided between the positive conductor and the inner wall of the aluminium cover tube.
This structural design is disadvantageous insofar as damage caused to the insulation between the positive conductor and the cover tube may lead to an internal short circuit. A resultant arc can normally not prevented by an ampere fuse.
It is the object of the present invention to provide a safe and reliable structural design of an electric heating device in the case of which not even a damaged insulation will cause an internal short circuit.
This object is achieved by the feature of claim 1.
According to the present invention, power is supplied to the PTC heating elements via respective electrode sheets arranged on both sides of the PTC elements. These electrode sheets each have connected thereto radiator elements for emitting the heat generated by the PTC heating elements. An electrically insulating layer is arranged between at least one of the electrode sheets and the respective radiator element.
In this way, a heating block can be prevented from comprising neighbouring radiator elements with different potentials between which a short circuit may occur. Due to the use of at least one insulating layer, the radiator elements are either potential-free or they have only one potential connected to them. A short circuit between radiator elements is therefore not possible.
Another advantage of this arrangement is that, if the insulating layer itself is damaged, this cannot yet lead to a short circuit, but that, in contrast to conventional heating devices, no short circuit will be caused and heating of the interior space will still be guaranteed.
The arrangement according to the present invention is also advantageous insofar as it has a particularly simple structural design.
According to an advantageous embodiment of the present invention, an additional insulating plate is inserted between adjoining radiator elements in a layered structure of an electric heating device comprising radiator elements and PTC heating elements. Such an insulating plate is especially inserted between adjoining radiator elements which are so configured that at least one of the radiator elements is kept potential-free by means of the electrically insulating layer according to the present invention.
One advantage of this embodiment is that the electrically insulating layer can be kept very thin so as to obtain a particularly good heat transfer, without there being any risk of short circuits, if damage is caused to the insulating layer, since a short circuit between neighbouring radiator elements is effectively prevented by the insulating plate. In this way, the operational safety and reliability of the electric heating devices according to the present invention can be increased still further.
According to another advantageous embodiment of the electric heating device according to the present invention, a single heating circuit consists of an arrangement of three radiator elements, a respective layer with PTC heating elements being arranged between these radiator elements. Due to the fact that the plus supply of the PTC heating elements is provided with an insulating layer in accordance with the present invention, the heating circuit can be subdivided into two separately controllable heating subcircuits.
An electric heating device can be formed of a plurality of such heating circuits, and the operation of said heating circuits can be finely subdivided in an arbitrary manner. In such a heating device, it can separately be decided for each heating circuit whether both heating subcircuits are to be controlled in common or separately.
One advantage of this embodiment is that an arbitrarily fine subdivision of the heating power of the individually controllable heating circuits can easily be adjusted. Even electric heating devices with high heating power can, in this way, be activated and deactivated without any noticeable load on the electric power supply of an automotive circuit.
Further advantageous embodiments represent the subject matters of subclaims.
In the following, preferred embodiments of the present invention will be explained in detail making reference to the figures, in which